Majin Vegeta and Fat Boo

[Evil Vegeta]

I think Goku was just holding-back effort, honestly. He was still getting accustomed to Super Saiyan 3, so I doubt he's actually suppressing his power while fighting Fat Boo.

I think the difference between Vegeta and Fat Boo is pretty huge, though. Vegeta only seems confident he'll be able to take Boo to "hell with him", and Kaioshin even acknowledges that Vegeta can't really do anything. I think Vegeta was able to pummel Boo because Boo didn't care enough to fight back.

 

[Let's Go Fearless!]

Yup, Boo was letting himself to get owned. It wasn't until he powered up twice which he didn't care holding back.

 

[Fantastische Hure]

I'd say he's closer to SSj3 Goku than he's to Majin Vegeta.

When he split into Pure-Evil Boo and Good Boo, his power was split, yet his way weaker half, Good Boo could still put up a better fight against Kid-Boo than SSj2 Vegeta could.

My opinion of-course.